1. Field of the Invention
The present invention relates to an image forming apparatus and a control method thereof, and, more particularly to an image forming apparatus employing an electrophotographic system and a control method thereof.
2. Description of the Related Art
In an image forming apparatus such as a copying machine employing an electrophotographic system, a process for developing an electrostatic latent image formed on a photoconductive drum using a toner or the like, transferring a toner image developed onto a recording sheet, and then heating and pressing the toner image with a fixing device to fix the toner image on the recording sheet is adopted.
As a structure of the fixing device, a form of using a heating roller having a heater built therein is often used. The toner image on the recording sheet is fixed by directly applying heat of the heating roller to the recording sheet or indirectly applying the heat to the recording sheet via a fixing belt or the like.
In order to secure satisfactory fixing performance, it is important to maintain the temperature of the heating roller within a predetermined range.
However, the temperature of the heating roller is low during starting of the image forming apparatus and immediately after the image forming apparatus is returned from a standby mode. Thus, in order to heat the heating roller using the heater to set the temperature of the heating roller within the predetermined temperature range, warm-up for a predetermined time is necessary. In order to reduce this warm-up time, there is a form of using an auxiliary heater in addition to a normal heater (hereinafter referred to as main heater).
In an image forming apparatus of this form, usually, a commercial power supply is used as a power supply for the main heater and a chargeable auxiliary power supply is mainly used as a power supply for the auxiliary heater. As the auxiliary power supply, for example, a structure that uses an electric double layer capacitor is often adopted.
When a voltage of the auxiliary power supply falls, it is necessary to charge the auxiliary power supply with the commercial power supply. However, if the driving of the main heater and the charging of the auxiliary power supply are simultaneously performed, it is likely that power consumption of the commercial power supply increases and exceeds a standard value of maximum power that can be supplied from one wall outlet (e.g., in the case of a general wall outlet in Japan, 1500 W (100 V, 15 A)).
Thus, for example, in JP-A 2004-200149, there is disclosed a technique concerning an inter-apparatus power cooperative system in which plural apparatuses (image forming apparatuses) having auxiliary power supplies are capable of exchanging electric power of the auxiliary power supplies with one another.
With this disclosed technique, even when an auxiliary power supply voltage of one apparatus (an apparatus A) falls and an auxiliary heater of the apparatus A cannot be used, since electric power of an auxiliary power supply of another apparatus (an apparatus B) is supplied to the auxiliary heater of the apparatus A, it is possible to simultaneously use a main heater and the auxiliary heater in the apparatus A. Consequently, it is possible to reduce a warm-up time.
However, in the inter-machine power cooperative system disclosed by JP-A 2004-200149, it is necessary to provide main power supplies and auxiliary power supplies with a charging function in the respective apparatuses. Thus, cost of the respective apparatuses increases.
Although a warm-up time is reduced for an apparatus that receives supply of electric power of an auxiliary power supply from another apparatus, for an apparatus that supplies the electric power of the auxiliary power supply, a warm-up time increases to the contrary compared with that in the case in which the electric power of the auxiliary power supply is not supplied to the power receiving apparatus.
In JP-A 2004-200149, there is also disclosed a form in which apparatuses exchange commercial power supplies via a dedicated power cable. In this form, as in the technique described above, for an apparatus that supplies electric power of a commercial power supply, since electric power that can be supplied to a heater of the apparatus itself falls compared with the case in which the electric power of the commercial power supply is not supplied to a power receiving apparatus, a warm-up time increases. In order to prevent such a situation, an auxiliary power supply for supplementing electric power of the commercial power supply supplied to the power receiving apparatus needs to be built in the apparatus that supplies the electric power. Then, cost increases because of cost of the auxiliary power supply.